A love story of a princess

A time jump of 15 years. The Princess, Lyra, lives in a specialized castle as imprisonment of the palace. The world-building focuses on the physical adaptations required for her life: clothes made of treated leather to prevent her skin from burning through silk, and a diet of raw minerals to sustain her demonic metabolism. She is isolated not by choice or "darkness," but by the very real danger due to some myth and misconception.